By Richard L. Gaw
Staff Writer 

Over the last several years, there has been a war waged in southern Chester County that has not equipped itself with the usual weaponry and armed forces, but rather, with the voices of residents, elected officials and some of the state’s most prominent experts in entomology.

It is a war against an insect that lives on average for five days, and whose maximum size reaches one-quarter inch – an invasive pest that rises out of the plumes and moistness of the region’s mushroom composting farms and reduces crop yields by up to 40 percent at the county’s more than 2,000 facilities, and permeates nearby homes that now resemble battlegrounds patrolled by angry citizens with vacuum cleaners and fly spray cannisters.

In short, these voices have collectively reached their respective boiling points on the Phorid Fly and are anxious to seek solutions to completely eradicate it from their lives and their businesses.

“I know many folks that have had Phorid Fly issues in their homes, that it feels to them like there has been no progress and things are worse than ever,” said Kennett Square Mayor Matt Fetick. “I have gotten emails in the last two weeks from residents, telling me that the infestation is worse this year than it was last year, which is why we’re not going to back away from doing everything we can to help solve the issue.”

Perhaps the most intense research about Phorid Fly mitigation efforts in the Commonwealth is being conducted by the Department of Entomology at Penn State University. On July 29 at Kennett Borough Hall, Fetick invited Dr. Michael Wolfin, the principal director of the department’s mushroom pest management team, to a focus group session, where he introduced several of his team’s current projects that aim to insecticides, fungicides, and herbicides labeled that have been approved for use in controlling Phorid Flies.

Attract and kill screens

In 2020, Wolfin and his team created an “attract and kill” method, which through the use of an electrostatically charged screen placed in mushroom growing rooms attracts flies emerging from the compost. The screens contain insecticide, which subsequently kills the flies when they touch the screen as they attempt to leave the growing room, preventing them from invading homes and mating to produce the next generation of flies.  

Attract and kill stations are particularly attractive because no pesticide is applied to the crop using this method. 

Using the technique of placing screens on windows at one test growing room, the team was able to kill over 900,000 flies over the first two weeks of the experiment. In the two weeks that followed, over 600,000 dead flies accumulated, and by early December, 99.9 percent of the mushroom flies were eliminated from the test room – mostly during the peak mushroom fly season from August to December.

In 2021, the team extended its outreach to 115 growing rooms and saw success at each growing room and is now set to install additional screens in 900 growing rooms.

Nematodes, predatory mites and beetles and insecticidal soaps

In 2023, using five growing rooms, the team began trials using Nematodes, nearly microscopic roundworms that dwell in mushroom soil and mushroom compost and are natural enemies of insects such as Phorid Flies. Nematodes enter the insect through breathing tubes, the mouth and the anus and form colonies, killing insects in the process.  Previous studies have identified that entomopathogenic nematodes can control mushroom sciarid flies, but mushroom phorids were too small for the Nematodes to penetrate.  Laboratory studies are ongoing to test smaller species of Nematodes to control mushroom phorid fly populations.

Using new application methods based on feedback from growers, the team continued the Nematobe lab trials in 2024, using 300-plus rooms with good results. Wolfin said the team recommends that new Nematodes be applied every four or five days, to provide a constant population of them in compost. 

“We found that if we apply Nematodes to compost, they killed more than 40 percent of the Phorid Flies in our lab studies, which doesn’t sound like a lot, but 40 percent is a lot more than zero,” he said. “These natural enemies are not in the farms, so the idea is to bring them into the farms.”

Wolfin said that the team has also done experiments with Predatory Mites, that live underground and eat soft-body insects. Preliminary laboratory studies suggest when applied appropriately, predatory mites may control up to 70 percent of the Phorid Fly populations at mushroom growing facilities.  

“A mite will kill eleven-and-a-half Phorid Fly larvae every three days, so if we’re applying 250,000 mites in a growing room, every three days you will see a dramatic loss of Phorid Flies,” he said. In similar experiments done with Predatory Beetles, the team determined that the insect kills about as many Phorid Flies as Predatory Mites.

Wolfin also introduced two organic insecticidal soap supplements – OrganiShield, an EPA-registered biopesticide that controls soft-bodied insects – and MycroSoap, which through application increases the efficiency of nutrient uptake by the mushroom, and has been proven to kill about 92 percent of Phorid Flies where it is applied. Wolfin said that MycroSoap is labeled for use as a supplement and can be applied to compost as a disinfectant.

Vestergaard netting

Wolfin then introduced a product made by Vestergaard, a Switzerland-based company that has created PermaNet®, long-lasting insecticidal nets (LLIN) that serve those in vulnerable situations around the world in protecting them from diseases like malaria. Thus far, the company has created the products SmartNet, PermaNet® 2.0 and PermaNet® 3.0, and has distributed more than 800 million nets around the world that have protected an estimated 1.6 billion people.

As of now, these nets are not used in the U.S. but are on the cusp of doing so for the first time – for the Chester County agricultural industry.

“Vestergaard decided that Pennsylvania mushrooms will be their first crop ever in the U.S. that they will get a label for,” Wolfin said. “These nets can be used for one to three years, and this happened very quickly. It can take over a year for a company to get registration, but because of the unfortunate state of emergency and the relative safety of the product, we were able to get a label in four months.”

Wolfin said that insecticidal nets have proven very effective in previous experiments and that during their first seven months of usage can kill 70 percent of Phorid Flies. 

“Vestergaard’s choice of choosing Pennsylvania mushrooms is to find something that demonstrates impact,” Wolfin said. “Eventually, they want to go beyond Pennsylvania mushrooms to bigger issues and bigger crops, but this is the highest impact issue they could find. They really want to come here and make people’s lives better.” 

“I will tell you that Vestergaard is a fantastic partner, because their goal is to get these nets in every farmer’s hands, make them as affordable as possible and prove that it works,” Fetick said. “Right now, their goal is, ‘How can we improve this in its concept?’” 

There is some good news for both mushroom farmers and the general public. Wolfin said that the Nematodes, mites and beetles are currently available for purchase; OrganiShield and MycroSoap are now available for use in Pennsylvania; and Vestergaard’s LLINs are now available for pre-order at Mushroom Central Supply, Inc., 1290 Baltimore Pike in Toughkenamon. 

State and municipal commitment

The local efforts to eradicate the Phorid Fly from private residences and mushroom operations in Chester County have been seen most prominently at both the municipality and state levels. Over the past year, New Garden Township, Kennett Township, Kennett Square Borough and Avondale Borough have all issued emergency declarations that have been forwarded to State Senators John Kane and Carolyn Comitta, and State Representatives Christina Sappey and John Lawrence.

In late January, State Agricultural Director Russell Redding issued a quarantine order to control Phorid Flies by making $500,000 in funding available through the Chester County Conservation District to farmers subject to the quarantine to help implement required treatment on their farms.

The order requires all mushroom growers in Kennett Township and New Garden Township to steam-treat mushroom houses and previously used growing medium between crops. Steam treatment kills adult flies, larvae, bacteria, fungus, and pathogens, preventing spread to adjacent farms or subsequent mushroom crops. The method is an industry-proven, effective practice for managing the spread of the pest.

“What we’ve learned in this process as we’ve talked to growers and gone farm to farm is that so many of our farms are doing everything that is expected of them, but a lot of farms don’t know what is expected and there hasn’t been accountability until now, but with the quarantine order, there now is,” said Sappey, who attended the meeting. “There is an education process happening now in the industry that is really helpful for the residents and the industry as a whole.”  

Sappey assured those in attendance that the increasing frustrations shared by both the mushroom industry and area residents is being heard by key stakeholders.

“Your government officials, your mayor, your townships, borough council and the mushroom industry all care about this issue,” she said. “We understand that this has been a nightmare to live with. The impact of what happened last fall – with the temperatures being higher than predicted last October – was a time when nature really forced our hand. When I think about where we started six years ago down in New Garden Township with people canvasing homes about the Phorid Fly issue to what we’re doing now, we’ve come a really long way.”

To learn more about the Phorid Fly mitigation efforts being done by the Entomology Department at Penn State University, visit  www.psu.edu/mushroomflyteam/

To learn more about Vestergaard and its products, visit www.vestergaard.com/products

To contact Staff Writer Richard L. Gaw, email [email protected].